【简答题】Who doesn’t love sitting beside a cosy fire on a cold winter’s night ? Who doesn’t love to watch flames (火苗) curling up a chimney? Fire is one of man’s greatest friends, but also one of his greatest e...
【简答题】The main reasons in respond to weld cracks are 1________ and 2_______, when The suce of welding work pieces is not cleared, and the flux is damp, the 3_______ in the weld metal may contribute to cr...